Mineral chemistry and petrogenesis of analcime crystals in igneous rocks from northeast of Meshkinshahr, NW Iran

Northeast  of Meshkinshahr, Eocene igneous rocks are exposed and are composed mainly of andesite, basalt, andesitic basalt, tephrite and is sometimes analcimite. The chemical composition of the rocks are in the range of alkaline rocks with high potassium and shoshsonitic affinity. Two main hypotheses are that they are either primary analcite or replacement pseudomorphous of leucite. Analcime crystals are usually large and eohedral to subhedral shaped phenocrysts coexisting with clinopyroxene in most rocks of this area. The presence of Ca-clinopyroxene and plagioclase rather than their sodic equivalents, presence of anhydrous mineral phases and lack of Na differentiation trend as well as partial alteration of the rocks likely supports the secondary growth of analcime either during cooling or after magma solidification.